At this point I wouldn't rule anything out. Treasure has released Gunstar Heroes on the PSN, IIRC, so it's not a total lost cause, IMO.

That's a little different, though, because that was released by SEGA, not Treasure.

Amusingly enough, that strengthens it in this case. If it were raised in the Radiant Silvergun thread there wouldn't be much hope, but this too IS a Sega release. Sega polled on whether people wanted it on PSN, and I believe it was Sega's order to port this rather than develop Guardian Heroes 2 to gauge interest and get more people in with the first game.

The real point that could deflate this is the fact Gunstar Heroes, IIRC, was running on Sega's (or Backbone's) Genesis emulator much like the other Genesis PSN/XBLA releases, not individually ported/remastered for the system like this was, so it could be a scenario where Treasure doesn't care/have enough experience to get it running optimally on the PSN and thus keeps it on XBLA.